Trigger circuits



Oct. 23 1951 WN 2,572,038

' TRIGGER CIRCUITS Filed May 5, 1949 INVENTOR. CLIFTON KINNE PatentedOct. 23, 1951 2,572,038 TRIGGER CIRCUITS Clifton B.- Kinne, Needham,Mas's. assignor t6 Interchemical Corporation, New York, N..Y., a

corporation of Ohio Application May 3, 1949, SerialNo. 91,104

This invention relates to an improvedthermionic trigger arrangement andmore particularly 1 Claim. (Cl. 250',27)

to a new trigger circuit having two thermionic tubes connectedasymmetrically with each other and comprising a third thermionic tube,whereby the output circuit is isolated from the input circuit andwhereby an output of high amplitude isobtainable at anuncommonly lowinput amplitude difierential.

Thermi-onic trigger circuits of the past have been built according tothe principle of the Eccles-J'ordanarrangement, as disclosed in BritishPatent 148,582, which is characterized mainly by a symmetric couplingoftwo thermionic tubes such as, for instance, from the anode of a firsttube to the control grid of a second tube and from the anode of thesecond tube to the control grid of the first. Or pentode trigger pairsare used for this purpose having the anode of the first tube connectedto the screen grid of the second tube and'the anode of the second tubeto the screen grid of the first. In response to a positive voltageapplied, one of the tubes becomes c-onducting. The ensuing potentialdrop in the anode circuit of this tube causes the potential between thegrid and the cathode of the other tube to become more negative and tohold this other tube non-conducting until the negative movement of theinput voltage sufiicient to raise the potential between the grid and thecathode of this other tube above a given minimum reverses the conditionsin that now this other tube conducts, thereby causing the potentialbetween the grid and the cathode of the first tube to become morenegative so that this tube is now rendered non-conducting until thesystem again reverts under the influence of the next succeeding increasein input voltage. In the well-known Schmitt trigger circuit coupling isfrom the anode of a first tube to the control grid of a second tube andfrom the cathode of the second tube to the cathode of the first tube.Some of the trigger arrangements mentioned need a negative voltagesupply in order to operate and some need compensating condensers if highspeed of response is required.

The thermionic trigger circuit of the present invention comprisesnumerous advantages not found in the aforementioned prior triggerarrangements. Thus, it provides for triggering in either direction fromone state of equilibrium to another at a lower hysteresis of the inputpotential; The output circuit is almost completely iso1'ated"fro'm' the"input circuit whereby the output stability is greatly improved. A supplyof negativevoltage.andthenecessity of using compensating condensers, is.entirely dispensed with. The circuit is. capable of operation at higherspeedland-of yielding an output signal of. higher amplitude. Inaddition, the present trig.-

ger circuit. is superior in. being adjustable by means of asinglecontrol and in being more simple inv construction.

Referring tothe accompanying drawing, one embodiment of the. triggercircuit is shown there which comprises threethermionic tubes, designatedas IE 25, and 30. i The tube I0 is prefer-- ably a pentodealthoughthe.suppressor grid 12 of a pentode is not; an absolute requirement for thehereindisclcsed purpose. The tubes 20 and,

3%) are preierablyftriodes, although multigrid tubes may. be used ifdesired. The tubes are connectedv in such a manner that a conductor isprovided between the anode I l of tube Ill and the control. grid 2-2 oftube. 20. Another conductor joins the anode. 2] of. tube 20 with thescreen grid: [3. of tube. It}. The tube 30' is made part of the triggerarrangement by connecting its cathode 33 toithe cathode 23 of tube 20and connecting, both cathodes tola common cathode resistor '10; theother end. of. which is connected to a ground conductor M. In thismanner it is possible to maintain the cathodes 23 and 33 of the secondand of the third tube, respectively, at all times at a substantiallypositive voltage which, in. turn, permits the direct. connectionbetweenthe control grid, 22 of the second tube with the anode H of the firsttube without the need of a source supplyingnegative voltage, providedthat the anode voltage. of tube It] is prevented from rising so high asto cause the grid,

22 of tube 20 to become more positive than its cathode 23. This can, be'doneby making the anode supplyvoltage of tube l-ll less than that oftube 26 by using a voltage divider such as the resistors. 4 4 and 59shown in the drawing or byother means well known in the art. The controlgrid 3?. of tube Bil. is held at a fixed potential, regulated; by apotentiometer M, or by other means, which serve the purpose of providinga control whereby the trigger arrange ment can be adjusted for thdesired input sensiativity or output amplitude. Whereas, according" gridM of tube 10. Thus, a practically complete separation is obtainedbetween input and output. The output voltage can be taken from otherpoints than 3! if complete isolation from the input is not essential.For example, an output from anode 21 of tube 20 will yield an output inthe same phase as the input. Plate current is supplied from the source43, the negative terminal of which is connected to the ground conductor41, and is carried to the anodes of the respective tubes throughconductors having the resistors 44, 45, and 46 inserted prior to theanodes. Other resistors are the resistor 48 between the anode 2| of tube20 and the screen grid I3 of tube l0, which may be made zero if desired,the resistor 49 from screen grid l3 of tube ill to ground, which may beomitted if the screen wattage of tube I is not exceeded, and theresistor 50 from control grid 22 of tube 20 to ground.

The principle of the invention will be understood when reading inconnection with the drawing the fo lowing description of what isbelieved to take place. The circuit arrangement has two states ofequilibrium. In the first state tube l0 i and tube 30 are passing verylittle anode current, while tube 20 is passing a large anode current. Inthe second state tube 20 is passing very little anode current, whiletubes l0 and 30 are passing a large anode current. Assuming, forpurposes of the present discussion, that at a given moment the inputpotential has decreased below a critical inferior triggering inputpotential and the trigger arrangement is in the first state ofequilibrium, where the tube 20 is passing a large anode current, thepotential of the grid l4 with respect to the cathode l5 of tube I0 ismore negative than the inferior critical voltage. As the input voltagebecomes more positive, the potential of the grid l4 of tube It!increases until a superior critical potential is reached, at whichpotential the circuit regenerates. That is, the anode voltage of tube Inin falling has reduced the grid voltage of tube 20,

reducing its plate current and raising its plate voltage which, in turn,raises the screen grid voltage of tube ID. This causes the anodepotential of tube i0 to fall still further. The regenerative actionoccurs almost instantaneously, being delayed only by the time requiredfor the stray capacity of the circuit to charge through the associatedresistance. After this regeneration the circuit is in the second stateof equilibrium, where tube is passin very little anode current. When theinput now reduces towards a negative potential, very little changeoccurs until the inferior critical potential is reached, where thecircuit again regenerates to the first state, in a manner analogous tothat described above. The tube operates in phase with tube l0, becausethe common cathode resistor by means of which tube 30 is coupled withtube 20 causes the anode current of tube 30 to decrease whenever theanode current of tube 20 increases. To obtain the largest possibleoutput amplitude at low input differential is a matter of selecting theresistors 40, 44, 45, 46, 48 and 49 and adjusting the potentiometer 4|.For example, with the circuit constants shown below, the yield is anoutput of volts at an input differential of 01 volt.

Tube I0 '6AK5 Tubes 20-1-30 6J6 Plate current supply 43 225 voltsCathode resistor 40 68,000 ohms Potentiometer 4i 50,000 ohms Resistor 4410,000 ohms= Resistor 45 2,500 ohms Resistor 46 5,000 ohm Resistor 48 0Resistor 49 Infinite Resistor 50 10,000 ohms The herein disclosedcircuit has also been madeto operate very satisfactorily by using a6AC7-' for tube [0 and GSN'? for tubes 20 and 30.

Since the potential of the grid 32 of tube 30 is adjusted to make thecircuit trigger properly, it is evident that by a different adjustmentof the potential of grid 32 the trigger circuit can be made inoperative.In many trigger circuit applications, such as counter circuits forinstance, it is desirable to render the circuit inoperative for certaintime intervals. This can be readily accomplished by coupling an externalsignal voltage onto the grid 32 to add or to subtract from the D. C.voltage as adjusted for proper triggering.

Ramifications of the circuit such as the one just described will beapparent to those skilled in the art, and the invention is not intendedto be limited to the exclusion of such ramifications.

In addition to the aforedisclosed intrinsic advantages, the new triggerarrangement is of enhanced usefulness in instances where the high speedswitching action of a trigger circuit is desired, but compactness andsimplicity are also required.

I claim:

A thermionic trigger arrangement comprising three thermionic tubes, eachhaving an anode, a cathode, and at least one control grid, the first ofthe said tube having in addition at least one auxiliary control grid, aninput circuit connected between the cathode and the control grid of thesaid first tube, circuit means interconnecting the anode of the saidfirst tube with the control grid of a second of the said three tubes andthe anode of the said second tube with the auxiliary control grid of thesaid first tube, circuit means, including a common cathode resistor,interconnecting the cathode of the said second tube with the cathode ofthe third of the said three tubes, means to hold the control grid of thesaid third tube at a fixed potential, anode current supply meansproviding a large anode current in said second tube when the inputpotential drops below an inferior critical level until it passes asuperior critical level, providing a large anode current in said firstand third tube when the input potential passes the superior criticallevel until it falls below the inferior critical level, and an outputcircuit comprising an impedance connected to the anode of the said thirdtube.

CLIFTON B. KINNE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,338,395 Bartelink Jan. 4, 19442,442,403 Flory et a1 June 1, 1948 2, 44,036 Crest June 29, 1948

